Many electronic devices include one or more rechargeable batteries that require external power to recharge from time to time. These devices may include cell phones, smart telephones, tablet computers, laptop computers, wearable devices, navigation devices, sports devices, health devices, accessory devices, and so on. Often, these devices are charged by connecting a charging cord to the electronic device and to an external power source (e.g., a wall outlet). The charging cord may be a cable having a connector with electrically conductive contacts that can mate with respective electrically conductive contacts of the electronic device. In some examples, electronic devices may use the received power to replenish the charge of an internal battery.
In some cases, the charging cord may be used exclusively for power transfer. In other cases, the charging cord may be used to transfer power alongside data. Examples of such connectors may include universal serial bus (“USB”), FireWire, peripheral component interconnect express (“PCIe”), or other similar data ports.
In many examples, a user may enjoy and regularly operate multiple electronic devices having internal batteries. These multiple devices often require separate charging cords having different power outputs and different connector types. Multiple charging cords can be burdensome to use, store, and transport from place to place. As a result, the benefits of device portability may be substantially limited.
Furthermore, charging cords may be unsafe to use in certain circumstances. For example, a driver of a vehicle may become distracted attempting to plug an electronic device into a vehicle charger. In another example, a charging cord may present a tripping hazard if left unattended.
To account for these and other shortcomings, some electronic devices may include an inductive charging system. A user may simply place an electronic device on an inductive charging surface to replenish the internal battery. A electromagnetic transmitter coil within the inductive charging surface may inductively couple to an electromagnetic receiver coil within the portable electronic device. By periodically toggling or alternating the current within the transmitter coil, a current may be induced in the receiver coil. The current induced in the receiver coil may be used to charge the internal battery of the portable electronic device.
However, in some situations, the current in the transmitter coil and/or in the receiver coil can produce a large amount of power or energy dissipation. When relatively small amounts of energy are transferred, energy dissipation can be large with respect to the amount of energy being transferred. Energy dissipation reduces the efficiency of the energy transfer and makes it difficult or time consuming to recharge the battery.